A plated steel sheet and a connection terminal material using same with low contact resistance and excellent corrosion resistance and adhesion of the coated film which is formed a coated film on a plated steel sheet surface using a stainless steel sheet as plated base sheet and a solution of post treatment including carbon black or graphite, carboxymethyl cellulose, and water borne organic resin composed from acrylic resin, polyester resin, urethane resin, or phenol resin is provided.
A plated steel sheet and a connection terminal material using same having low contact resistance, which is treated by diffusion treatment after nickel plating at the lower layer and tin plating thereon in case of post treatment method of stainless steel sheet, and which is treated using a water-soluble solution of post treatment including carbon black or graphite, carboxymethyl cellulose, water borne organic resin such as acrylic resin, polyester resin, urethane resin, or phenol resin.
The present invention relates to a surface treated steel sheet and a terminal material used thereof with superior conductivity, steadiness of conductivity after aging a lapse of time, corrosion resistance, and adhesion and low contact resistance using a stainless steel sheet as a plated base sheet.
Conventionally, a combination of carbons has been mainly used for electric connection terminal materials from the viewpoints of conductivity and corrosion resistance. Since a combination of carbons is expensive, a combination of carbon and a metal sheet has been investigated also from the viewpoint of workability. However, is has a problem of a drastic decrease of conductivity after aging due to a formation of oxide or hydroxide on the metal sheet surface.
In order to solve the problem mentioned-above, electric connection terminal materials having lower price than that of carbon and similar conductivity as that of carbon have been required.
Although using only metal material for an electric connection terminal material can be economical, it has been a problem to actually do so because of poor corrosion resistance and low conductivity due to the formation of oxide or hydroxide on the surface after aging. Although a stainless steel sheet with superior corrosion resistance used can show good corrosion resistance, it has a problem of conductivity due to the formation of strong bonded oxide on the surface
Taking these problems into account, it is a technical objective of the present invention to provide a surface treated steel sheet and a connection terminal material produced thereof with superior conductivity, steadiness of conductivity after aging, corrosion resistance, and adhesion and with low contact resistance using a plated steel sheet which is a multi-layer plated steel sheet treated with diffusion having nickel plated layer at the lower layer and tin plated layer thereon on a stainless steel sheet as a plated base sheet.
The present invention has the characteristics of using a plated steel sheet treated with diffusion, which has nickel plated layer at the lower layer and tin plated layer thereon on a stainless steel sheet as plated base sheet, and having low contact resistance formed a coated film on a surface, including carbon black or graphite, carboxymethyl cellulose, and water borne organic resin.
It also has the characteristics of using a plated steel sheet treated with diffusion, which has nickel plated layer at the lower layer and tin plated layer thereon on a stainless steel sheet as plated base sheet, and having low contact resistance formed a coated film on a surface, including carbon black or graphite, carboxymethyl cellulose, water borne organic resin, and cross-linking agent of the water borne organic resin.
It is desirable that these surface treated steel sheets have any one of water borne organic resin such as acrylic resin, polyester resin, urethane resin, or phenol resin.
Moreover, a connection terminal having the characteristics of the surface steel sheet of the present invention, can be used for the contact part with carbon in an electric connection terminal.
When a plated steel sheet having nickel plated layer at the lower layer and tin plated layer thereon on a stainless steel sheet as plated base sheet, which has been diffusion treated after these plating, is treated using a water-soluble solution of post treatment including carbon black or graphite, carboxymethyl cellulose, and water borne organic resins composed of acrylic resin, polyester resin, urethane resin, or phenol resin, deposited coated film, to prevent oxidation of the surface of the plated steel, shuts off oxygen in the air by avoiding the formation of an oxide film, which causes deterioration of conductivity, and suppresses deterioration of conductivity and corrosion resistance. Moreover, diminution of conductivity due to deposition of coated film is hardly observed, since the coated film contains carbon black or graphite having superior conductivity.
The operation mode of the present invention will be described in further detail mentioned below.
A stainless steel sheet is used as plated steel sheet. Iron-chromium stainless steel such as martensitic or ferritic stainless steel and iron-nickel-chromium stainless steel such as austenitic, austenitic-ferritic, martensitic, or semiaustenitic stainless steel can be used as stainless steel sheet. A plated steel sheet having nickel plated layer at the lower layer and tin plated layer thereon on a stainless steel sheet, which has been diffusion treated after these plating, can be selected. The plated steel sheet uses a stainless steel sheet as plated base sheet and it is preferable to use as connection terminal of lead storage battery or fuel cell which is easily exposed to acid atmosphere, because nickel-tin alloy which has superior chemical resistance exists on the surface layer of the plated layer. A suitable amount of plating is 0.3-30 g/m2 of the total amount of nickel and tin plating. Plating amount of less than 0.3 g/m2 is not preferable in case of performing the diffusion treatment after the plating, because the conductivity decreases extremely due to the diffusion of chromium in the surface layer which is a component of the stainless steel sheet. Plating amount over 30 g/m2 is not favorable from economical point. Although the ratio of the amount of nickel plating and tin plating is not particularly limited, the amount of nickel plating of not less than two to that of tin plating of one is specially preferable from the viewpoint of corrosion resistance of the plated layer. The diffusion treatment is performed under nitrogen gas, hydrogen gas, mixed gas of nitrogen and hydrogen, or argon gas atmospheric condition without containing oxygen, and the heating temperature is preferable in the range of 400 to 600xc2x0 C. From the viewpoint of contact resistance, the heating time is preferable in the range of a certain time without chromium diffusion which increases contact resistance or iron diffusion on the surface which causes rust.
The diffusion treated steel sheet after the plating is treated with a solution containing carbon black or graphite of 10-350 g/l, carboxymethyl cellulose of 0.1-40 g/l, and water borne organic resin of 1-200 g/l as solid matter composed from acrylic resin, polyester resin, urethane resin, or phenol resin.
Carbon black includes channel black, furnace black, acetylene black, or Katchen black. Graphite includes artificial graphite, flake graphite, flaky graphite, or amorphous graphite. The concentration of less than 10 g/l is insufficient for conductivity while the concentration above 350 g/l deteriorates dispersion of graphite extremely.
Any one type of water borne organic resin can be used, preferably water-soluble, water-dispersed, or emulsion type resin.
Water borne acrylic resin includes acrylic acid, acrylic acid ester, acrylamide, acrylonitrile, methacrylic acid, and polymer and copolymer of methacrylic acid esters. As functional group of ester, carboxyl group, amino group, methyl group, ethyl group, butyl group, amyl group, ethylhexyl group, or octyl group are included. Water borne ethyleneacrylic resin containing ethylene group can be also included.
Water borne polyester resin may be water-dispersed material by polyoxyethylene nonylphenylether, polyoxyethylene nonylphenylether sodium sulfate, sodium lauryl sulfate, or rosined soap, may be ones having hydrophilic radical including such as carboxyl group, sulfone group, sulfuric ester group, phosphoric ester group, amino group, ammonium salt, hydroxyl group, ether group, or amide group, or may be ones including alkyd resin, maleic acid resin, or unsaturated polyester.
Water borne urethane resin which has water-soluble COOH group or amine group in terminal group is included.
Water borne phenol resin includes resol type ones produced by reaction of phenol and formaldehyde under alkali catalyst.
In terms of water borne organic resin composed of acrylic resin, polyester resin, urethane resin, or phenol resin, the solid matter concentration of less than 1 g/l produces insufficient corrosion resistance, while the concentration exceeding 200 g/l produces drastic decrease of conductivity and increase of viscosity of treatment solution, making the uniform treatment difficult. Moreover, the cross-linings agent of the water borne organic resin above-mentioned can be added 0.1-20% to the solid matter of the said water borne organic resin. Table 1 shows types of usable cross-linking agent for the said water borne organic resin.
When the concentration of the cross-linking agent above-mentioned is less than 0.1% to the solid matter concentration of the said water borne organic resin, there is no effect for adhesion. On the other hand, when the concentration is above 20%, the water borne organic resin above-mentioned is cross-linked rapidly and the precipitate is produced, and the stability of the treatment solution is deteriorated in a lapse of time.
Carboxymethyl cellulose containing sodium, potassium, or ammonium can be used. The concentration of carboxymethyl cellulose of less than 0.1 g/l produces deteriorated film of forming property or adhesion while the concentration over 40 g/l produces drastic decrease of dispersion.
The coating method may be but is not limited to spray coating, roll coating, knife coating, curtain flow coating, or reduction of area by roll or air knife after dip coating.
A suitable thickness dried of post treatment film is 0.02-10 xcexcm. Since the thickness of less than 0.02 xcexcm cannot cover the plated surface uniformly, corrosion resistance and conductivity is deteriorated in a lapse of time. When the thickness is over 10 xcexcm, corrosion resistance tends to improve but conductivity is saturated, which is not economically preferable.